1. Technical Field
The present invention relates to a cleaning liquid and a cleaning method using the liquid. More specifically, it relates to a cleaning liquid used in a cleaning step of a substrate for use in semiconductor devices after planarization by chemical mechanical polishing (hereinafter simply referred to as “CMP”) in the manufacture of semiconductor devices, and a cleaning method using the cleaning liquid.
2. Related Art
In the development of semiconductor devices typically represented by semiconductor integrated circuits (hereinafter sometimes referred to as “LSI”), generally a shallow trench isolation (STI) film, also referred to as a device isolation film, is often formed first at a lower portion on a substrate, and a multilayer laminate structure, in which layers such as a insulating film or a metal film are laminated in multiple layers, is formed thereabove. When laminating the multilayer, in addition to an interlayer insulating film usually used such as p-TEOS, O3-TEOS, etc., a step of depositing an interlayer insulating film (ILD film) containing, for example, a low insulating constant interlayer film with a specific insulating constant of about 3.5 to 2.0 (including, for example, an organic polymer type, a methyl group-containing silica type, an H—Si containing silica type, an SiOF type, a porous silica type, and a porous organic material type usually referred to simply as Low-k film) or a metal film on a substrate is generally conducted, followed by application of a planarizing treatment by CMP of resultant unevenness and stacking of a new wiring on the planarized surface. In recent years, along with the progress of miniaturization of the size of semiconductor devices, planarization at high accuracy in each of the layers of the substrate has become increasingly necessary.
Therefore, great expectations have been placed on the CMP planarization step (CMP step) and the relative importance of the CMP step as a part of the entire semiconductor device manufacturing process has been increased. Further, a cleaning step of a substrate for a semiconductor device applied after the CMP step also has an important role.
The cleaning step is a step conducted with an aim of removing a targeted amount of polished metals (contaminant metals), a portion of abrasive grains (contaminant particles), and organic residues remaining on the surface of a substrate for use in semiconductor devices after the CMP step. As a cleaning liquid used in the cleaning step, a cleaning liquid containing specific surfactants and alkalis or organic acids (refer, for example, to Japanese Patent Application Laid-Open (JP-A) No. 2003-289060), a cleaning liquid with organic acids, organic alkalis, and surfactants added thereto (refer, for example, to JP-A No. 2005-260213) and the like have been proposed.
However, from the viewpoint of efficiently removing organic residues or fine particles of abrasive grains from the surface of the substrate for use in semiconductor devices after the CMP step, there is still room for improvement. For example, water at high pressure jetted out from a nozzle tip in the cleaning step generates a large amount of mist at the surface of the semiconductor substrate. While most of this is discharged from an exhaust port, a considerable portion thereof is suspended in a chamber and the suspended mist is deposited back onto the substrate surface of the semiconductor device. Such mist often contains dust in the gaseous phase by adsorption, and when the water content of the mist evaporates after deposition, the dust remains adhered to the surface of the semiconductor substrate, which sometimes makes removal thereof difficult. Further, even when mist not containing dust is adsorbed on the surface of the semiconductor substrates and the water evaporates, traces of the mist sometimes remain as a water mark.
Further, for the cleaning step after the CMP step for a device substrate for use in a semiconductor formed with copper wirings, when using an acidic cleaning liquid (hydrochloric acid or hydrofluoric acid) hitherto usually used as a cleaning liquid for a substrate for use in a semiconductor device, not only the copper oxide deposited on the insulating film but also the metallic copper of the wiring are dissolved to cause problems of corrosion or disconnection of the wiring, such that the use of an acidic cleaning liquid is not preferable.
For the removal of organic or inorganic materials as impurities and particles such as abrasive grains, while it has been thought that an alkaline cleaning liquid causing electrostatic repulsion between the wafer surface and the particles is effective, when using a cleaning liquid containing sodium hydroxide, potassium hydroxide or the like, containing metal ions as an alkali source, a problem has resulted that such metals are adsorbed onto the surface of the insulating film (silicon oxide) to deteriorate the insulation properties. Further, among the alkaline cleaning liquids, since an inorganic alkali cleaning liquid not containing metal ions (such as aqueous ammonia) has a strong dissolving effect on copper, it cannot be used in the cleaning of a device substrate for use in semiconductors formed with copper wirings.
On the other hand, while a cleaning liquid containing quaternary ammonium has an advantage of not corroding copper wirings and has high particle removal effect, since quaternary ammonium is strongly alkaline, it has a strong etching effect on the insulating film and has the drawback of roughing the surface of a device substrate for semiconductors planarized in the CMP step. It is known that in order to solve such a problem the etching rate can be retarded by the addition of hydrogen peroxide to the quaternary ammonium. This, however, results in a problem that the oxidization power of the hydrogen peroxide oxidizes the surface of the copper wiring to worsen the conductivity.
As described above, while there is a need for a cleaning liquid used in the cleaning step of a substrate for use in semiconductor devices after the CMP step that do not corrode or oxidize copper wirings when applied to the surface of a semiconductor substrate having copper wirings, and that are capable of removing impurities remaining on the surface of a semiconductor substrate without roughening the surface, such a cleaning liquid has not yet been provided.